Heretofore, resistor units have been employed as components of switching systems for adjusting the speed of blower motors for automotive heating and ventilating systems which may also include air conditioning. In a known resistor unit construction, several resistors are connected to and supported by electrical terminals mounted on a terminal head plate. The terminals generally have prongs or lugs which extend forwardly through the plate for receiving an electrical receptacle or connector, whereby the resistors are connected into a switching circuit for selectively connecting the resistors in series with a blower motor for reducing the speed of the motor.
Typically, the resistor unit is mounted on a supporting wall which constitutes one wall of the blower casing or a wall of a duct through which air is directed by the blower. The resistors extend through an opening in the supporting wall and are positioned in the blower casing or a duct connected to the casing, so that the resistors are immersed in the flow of air from the blower. In this way, the resistors are cooled by the flow of air, and the air is heated to some extent by the resistors.
The prevailing practice has been to employ screws or other fasteners to secure the terminal head plate of the resistor unit to the supporting wall. However, the use of such fasteners has the disadvantage that a fastener is sometimes dropped into the blower casing or duct through the opening therein. As a worst case, a dropped fastener may become lodged between the casing wall and the rotor or wheel of the blower, so that the rotor is locked and becomes inoperative. In this case, an expensive repair must be made to locate and remove the offending fastener.
Even if the fastener falls into a harmless place in the blower casing, the retrieval of the fastener may be very difficult so that the installer will not remove the dropped fastener. In that case, the dropped fastener will produce an annoying rattle throughout the life of the vehicle in which the blower is installed.